1. Field of the Invention
The invention relates to an indexable insert of hard metal or cermet with a multi-layer surface coating for cutting objects essentially made of metal.
The invention relates in particular to a cited indexable insert for a machining of parts of a polyphase material, such as casting alloys and the like.
2. Discussion of Background Information
In a cutting of workpieces made essentially of metallic materials, a sudden improvement in capacity was associated with the introduction of hard-metal or cermet tools which led to the development of indexable inserts in clamp holders.
The next sudden increase in tool capacity, possibly associated with an improvement in the quality of the machining surface, was generated by a coating of the surfaces of the indexable inserts with hard materials, such as nitrides, carbides, oxides and mixed forms thereof.
In order to further increase cost-effectiveness and surface quality in metal cutting, further developments took place in coating technology in layer composition and in layer thickness optimization.
The demands made on the surface coating of indexable inserts lie in principle in a high adhesion to the substrate and a reduction of the mechanical and thermal stress on the hard metal substrate.
For example, a hard metal cutting tool is known from EP A 1 348 779 with which a tough (bonding) zone close to the surface is produced on the hard metal substrate. A multi-layer coating of titanium nitride and/or titanium-carbo-nitride, α-Al2O3, titanium-carbo-nitride or titanium-oxi-carbo-nitride with a titanium nitride outer layer in respectively determined thicknesses and thickness proportions is applied to this zone in order to achieve the high wear resistance and toughness of the tool.
According to the general technical knowledge of one skilled in the art in the field of coated indexable inserts, a tough surface bonding zone on the substrate and a multi-layer coating with a titanium nitride cover layer having a high hardness and wear resistance promotes the tool quality.